n=int(input())
c=input()

r_cnt=c.count('R')
w_cnt=c.count('W')

last_c='R'*r_cnt+'W'*w_cnt

num=0
for i in range(n):
  if c[i]!=last_c[i]:
    num+=1

print((num+2-1)//2) n=int(input()) n int(input()) int input() input c=input() c input() input r_cnt=c.count('R') r_cnt c.count('R') c.count c count 'R' w_cnt=c.count('W') w_cnt c.count('W') c.count c count 'W' last_c='R'*r_cnt+'W'*w_cnt last_c 'R'*r_cnt+'W'*w_cnt 'R'*r_cnt 'R' r_cnt 'W'*w_cnt 'W' w_cnt num=0 num 0 for i in range(n):
  if c[i]!=last_c[i]:
    num+=1 i range(n) range n if c[i]!=last_c[i]:
    num+=1 c[i]!=last_c[i] c[i] c i last_c[i] last_c i num+=1 num 1 print((num+2-1)//2) print (num+2-1)//2 num+2-1 num+2 num 2 1 2 num+=1 1 num n=int(input()) int(input()) n c=input() input() c r_cnt=c.count('R') c.count('R') r_cnt w_cnt=c.count('W') c.count('W') w_cnt last_c='R'*r_cnt+'W'*w_cnt 'R'*r_cnt+'W'*w_cnt last_c num=0 0 num
n=int(input())
c=input()

r_cnt=c.count('R')
w_cnt=c.count('W')

last_c='R'*r_cnt+'W'*w_cnt

num=0
for i in range(n):
  if c[i]!=last_c[i]:
    num+=1

print((num+2-1)//2)